Application of specific electrical fields to spinal nerve roots, spinal cord, and other nerve bundles for the purpose of chronic pain control has been actively practiced since the 1960s. While a precise understanding of the interaction between the applied electrical energy and the nervous tissue is not fully appreciated, it is known that application of an electrical field to spinal nervous tissue (i.e., spinal nerve roots and spinal cord bundles) can effectively mask certain types of pain transmitted from regions of the body associated with the stimulated tissue. More specifically, applying particularized electrical energy to the spinal cord associated with regions of the body afflicted with chronic pain can induce paresthesia, or a subjective sensation of numbness or tingling, in the afflicted bodily regions. This paresthesia can effectively mask the transmission of non-acute pain sensations to the brain.
It is known that each exterior region, or each dermatome, of the human body is associated with a particular spinal nerve root at a longitudinal spinal position. Thus, the head and neck regions are associated with C2-C8, the back is from C2-S3, the central diaphragm is between C3 and C5, the upper extremities are between C5 and T1, the thoracic wall is between T1 and T11, the peripheral diaphragm is between T6 and T11, the abdominal wall is associated with T6-L1, lower extremities are located from L2 to S2, and the perineum from L4 to S4. By example, to address chronic pain sensations that commonly focus on the lower back and lower extremities, a specific energy field can usually be applied to a region between bony level T8 and T10. As should be understood, successful pain management and the avoidance of stimulation in unafflicted regions necessarily requires the applied electric field to be properly positioned longitudinally along the dorsal column.
Positioning of an applied electrical field relative to a physiological midline is equally important. Nerve fibers extend between the brain and a nerve root along the same side of the dorsal column as the peripheral areas the fibers represent. Pain that is concentrated on only one side of the body is "unilateral" in nature. To address unilateral pain, electrical energy is applied to neural structures on the side of a dorsal column that directly corresponds to a side of the body subject to pain. Pain that is present on both sides of a patient is "bilateral." Accordingly, bilateral pain is addressed through either an application of electrical energy along a patient's physiological midline or an application of electrical energy that transverses the physiological midline.
Pain managing electrical energy is commonly delivered through electrodes positioned external to the dura layer surrounding the spinal cord. The electrodes are carried by two primary vehicles: a percutaneous catheter and a laminotomy lead.
Percutaneous catheters, or percutaneous leads, commonly have three or more, equally-spaced electrodes, which are positioned above the dura layer through the use of a Touhy-like needle. For insertion, the Touhy-like needle is passed through the skin, between desired vertebrae, to open above the dura layer.
For unilateral pain, percutaneous leads are positioned on a side of a dorsal column corresponding to the "afflicted" side of the body, as discussed above, and for bilateral pain, a single percutaneous lead is positioned along the patient midline (or two or more leads are positioned on each side of the midline).
Laminotomy leads have a paddle configuration and typically possess a plurality of electrodes (for example, two, four, eight, or sixteen) arranged in one or more independent columns. For each column having more than one electrode, the electrodes for such columns are equally spaced. An example of a sixteen-electrode laminotomy lead is shown in FIG. 1.
Implanted laminotomy leads are commonly transversely centered over the physiological midline of a patient. In such position, multiple columns of electrodes are well suited to address both unilateral and bilateral pain, where electrical energy may be administered using either column independently (on either side of the midline) or administered using both columns to create an electric field which traverses the midline. A multi-column laminotomy lead enables reliable positioning of a plurality of electrodes, and in particular, a plurality of electrode columns that do not readily deviate from an initial implantation position.
Laminotomy leads require a surgical procedure for implantation. The surgical procedure, or partial laminectomy, requires the resection and removal of certain vertebral tissue to allow both access to the dura and proper positioning of a laminotomy lead. The laminotomy lead offers a more stable platform, which is further capable of being sutured in place, that tends to migrate less in the operating environment of the human body.
Percutaneous leads require a less-invasive implantation method and, with a plurality of leads, provide a user the ability to create almost any electrode array. While likely more stable during use, laminotomy leads do not offer an opportunity for electrode array variance due to the fixed nature of their electrode arrays. It is common practice that the electrodes of both percutaneous leads and laminotomy leads are equally spaced in a longitudinal direction.
A maximum number of electrodes for a lead, whether percutaneous or laminotomy, is dictated by known stimulation systems. Current stimulation systems (not shown) enable 4-stimulation channels, 8-stimulation channels, or 16-stimulation channels, where each "channel" represents a controllable electrical output. Thus, conventional stimulation leads include at least two but no more than 16 electrodes, wherein each electrode is respectively coupled to a single stimulation system output. Given that the number of electrodes of conventional stimulation leads are determined by a coupled stimulation system (as opposed to a patient's physical condition), the provision of equal, longitudinal spacing between such electrodes results in limited effective stimulation lengths.
To this end, a significant number of spinal cord stimulation cases for the management of pain involve a combination of lower back and leg pain. To address these particular regions, it is desirous to target electrical energy between the pedicles of T8 and T9 (lower back) and T10-L1 (depending on the particular leg segment). Due to the distance between these sites and the complex nature of such pain, it is necessary to use multiple leads, whether of a percutaneous form and/or a laminotomy form.
Consequently, a need exists for a laminotomy lead that, within the arbitrary boundaries of conventional stimulation systems, can provide a greater effective stimulation length to enable delivery of electrical energy over a greater range of spinal nervous tissue. To this end, a further need exists for a laminotomy lead that is capable of addressing complex pain commonly affecting the lower back and legs.